In this project we are studying how intimal thickening develops in polytetrafluoroethelyne arterial grafts (PTFE) and in injured arteries in baboons. In the last year we pursued the hypothesis that nitric oxide (NO) is a major negative regulator of smooth muscle cell (SMC) growth in blood vessels, because high blood flow suppresses intimal thickening and induces the endothelial nitric oxide synthase gene (ecNOS). Our experiments with agents to block ecNOS cause vasoconstriction but do not induce SMC proliferation unless there is some degree of injury. In addition, we have performed experiments with antibodies to platelet derived growth factor receptor-( and ( (PDGF-R-( and () to define a role for PDGF in intimal thickening. PDGFR-( blockade inhibits intimal thickening induced by injury or a switch in blood flow. PDGFR-( blockade does not inhibit intimal hyperplasia but may cause cell death. We are currently working on the problem of how high blood flow causes regres sion of intimal thickening and are testing the hypothesis that NO may be causing smooth muscle cell apoptosis. We have also tried to extend our work to clinical application. We have developed an explant system and have shown that SMC growth in explants resembles very closely SMC growth in injured artery. We now hope to use the explant system to define the properties of human SMCs in saphenous vein explants. The ultimate goal is to provide a link between animal studies and outcome in humans. FUNDING NIH grants RR00166, HL30946, and HL18645. Hedin, U., Daum, G., and Clowes, A.W. Heparin inhibits thrombin-induced mitogen-activated protein kinase signaling in arterial smooth muscle cells. J. Vasc. Surg. 27:512-520, 1998. Daum, G., Kalmes, A., Levkau, B., Wang, Y., Davies, M.G., and Clowes, A.W. Pervanadate inhibits mitogen-activated protein kinase kinase-1 in a p38MAPK-dependent manner. FEBS Lett. 427:271-274, 1998. Daum, G., Levkau, B., Chamberlain, N.L., Wang, Y., and Clowes, A.W. The mitogen-activated kinase pathway contributes to vanadate toxicity in vascular smooth muscle cells. Molec. Cell. Biochem. 183:97-103, 1998. Clowes, A.W. Vascular surgery and vascular gene therapy. J. Cardiovasc. Surg. 39(Suppl 1) 185-188, 1998. Koyama, N., Kinsella, M.G., Wight, T.N., Hedin, U., and Clowes, A.W. Heparan sulfate proteoglycans mediate a potent inhibitory signal for migration of vascular smooth muscle cells. Circ. Res. 83:305-313, 1998. Mattsson, E.J.R., Geary, R.L., Kraiss, L.W., Vergel, S., Liao, J.K., Corson, M.A., Au, Y.P.T., Hanson, S.R., and Clowes, A.W. Is smooth muscle growth in primate arteries regulated by endothelial nitric oxide synthase? J. Vasc. Surg. 28:514-521, 1998. Fischer, J.W., Davies, M.G., Wight, T.N., and Clowes, A.W. Versican is the predominant proteoglycan in flow accelerated neointimal hyperplasia of endothelialized baboon vascular grafts. Circulation 98 (17 suppl. I) 228, 1998 (abstract).